At least 48 people were killed today when a suicide bomber blew himself up inside a mosque, during Friday prayers, in Pakistan's volatile north-west.

The blast demolished the two-storey mosque in Jamrud, near the Afghan border. Many of the dead and injured were buried under bricks and other debris.

Officials warned that up to 70 could have died. Hundreds of local people gathered to dig out the victims by hand, carrying many away on beds, used as makeshift stretchers.

Jamrud lies in the Khyber part of Pakistan's tribal area, with few medical or rescue facilities.

The injured were taken to hospitals in Peshawar, around 20 miles away. Locals took many of them in their own cars, while ambulances were dispatched from Peshawar.

Tariq Hayat Khan, the top official in the Khyber region, said that the bomber denoted himself as soon as the imam said "God is Great" to begin the weekly Friday prayers at lunchtime.

Between 200 and 250 worshippers were in the mosque at the time, including many paramilitary soldiers from a nearby military checkpoint who may have been the target of the attack.

Khan said that 48 dead and 70 injured had been counted so far, but added that the death toll could rise to 70.

"Everybody says that a Muslim could not have done this," said Khan. "This is the work of kaffirs [infidels]."

Jamrud lies on the road through Khyber used by Nato to take the majority of its supplies to troops in Afghanistan.

Khyber used to be the safest and most stable part of the tribal area but it has come under sustained assault from Islamic militants in recent months. Last week a rocket attack in the area killed 11.

"The tribal people and all Pakistanis have to boldly face these challenges," said Noor-ul-Haq Qadri, the local MP. "I don't understand who these people [the bombers] are or what they want."

There is an ongoing, if fitful, Pakistani military operation to secure Khyber, which borders the provincial capital, Peshawar. A campaign of suicide bombings, starting in summer 2007, has torn Pakistan apart.

Yesterday, there was a suicide attack at a restaurant near the town of Tank, also in north-west Pakistan, that killed at least 11. The tribal area is a stronghold for Taliban and al-Qaida militants.

The latest attack came as the Obama administration was due today to unveil its new Afghanistan and Pakistan strategy, aimed at stemming the violence and eliminating terrorist bases in western Pakistan.